The invention concerns a sealing ring for a rotary shaft which serves to retain and/or return a lubricant, comprising a generally annular supporting member made of a relatively rigid material and a generally annular sealing member made of an elastic material and connected to the supporting member. The sealing member includes a sealing lip projecting radially inward toward the shaft. The end of the sealing lip is terminated by a sealing surface which when the sealing ring is assembled to the shaft, is in contact with the shaft along a contact surface. One side of the sealing surface is directed toward the lubricant and the other side toward the atmosphere. On the atmospheric side of the sealing surface, spaced apart projections are formed on the lip and the bottom surface of each of these projections rests against the shaft surface in the assembled unit. The contacting surfaces of the projections with the shaft are limited by at least one edge which runs from a point lying at a distance from the adjacent limiting edge of the contact surface of the sealing edge obliquely toward said limiting edge with inclusion of an acute angle. Such a sealing ring is disclosed in U.S. Pat. No. 3,868,105.
A sealing ring of this type is called a hydrodynamic sealing ring because, when the shaft rotates, the projections produce a hydrodynamic effect whereby lubricant which has nevertheless inevitably leaked to the outside, between the sealing surface of the sealing lip and the periphery of the shaft, as a result, for example, of wear on the shaft and/or on the sealing lip, or because particles of dirt have been trapped between the sealing surface and the shaft, is again returned to the margin of the lubricant, so that no lubricant is lost.
The sealing lip which is pressed against the shaft, however, is subject to relatively great frictional forces, whence the lip wears relatively rapidly and must be replaced after a comparatively short time. Moreover, temperature elevations likewise occur, causing the sealing ring to age relatively quickly.